A Direct Bicarbonate Detection Method Based on a Near-Concentric Cavity-Enhanced Raman Spectroscopy System

Area of Science:

• Hydrothermal science
• Oceanography
• Analytical chemistry

Background:

• Raman spectroscopy offers potential for hydrothermal science but suffers from low sensitivity.
• Limited sensitivity restricts its application in marine environments, particularly for detecting key ions like bicarbonate.

Purpose of the Study:

• To develop a highly sensitive Raman spectroscopy system for direct bicarbonate detection in seawater.
• To overcome the limitations of conventional Raman spectroscopy in marine applications.

Main Methods:

• Development of a near-concentric cavity-enhanced Raman spectroscopy (CE-RS) system.
• Implementation of a specialized data processing scheme to isolate weak bicarbonate signals from strong sulfate interference.
• Direct detection and quantification of bicarbonate (HCO₃⁻) in seawater samples.

Main Results:

• Achieved a significantly enhanced detection of bicarbonate (HCO₃⁻) using the CE-RS system.
• Determined a limit of detection (LOD) of 0.37 mmol/L for bicarbonate, well below typical seawater concentrations.
• Enabled quantitative analysis with a high coefficient of determination (R² = 0.951) after signal extraction.
• Measured bicarbonate concentration in deep-sea samples at 1.91 mmol/L with a 2.1% relative error compared to established values.

Conclusions:

• The developed near-concentric cavity-enhanced Raman spectroscopy system successfully enables direct and sensitive detection of bicarbonate in seawater.
• This technology overcomes previous sensitivity limitations, paving the way for accurate in-situ monitoring of seawater chemistry.
• Future development could lead to real-time, in-situ ocean observation systems for crucial marine chemical parameters.